Image forming apparatuses employing a conveying belt that supports and conveys sheets of paper for image formation are well known in the art. One such image forming apparatus disclosed in U.S. Patent Application Publication No. 2004/253013 (corresponding to Japanese Patent Application Publication No. 2004-294471) forms toner images on paper using a process unit for transferring the toner onto the paper as the paper is supported on a surface of the conveying belt and conveyed in a predetermined direction.
In the image forming apparatus described in U.S. Patent Application Publication No. 2004/253013, the conveying belt is a seamless, endless belt. A plurality of the process units is arranged along the conveying direction of the belt with each process unit disposed in confrontation with the surface of the conveying belt. The process units accommodate toner in one of the colors cyan, magenta, yellow, and black to support multicolor image formation.
The image forming apparatus disclosed in U.S. Patent Application Publication No. 2004/253013 performs a calibration process to correct problems in color registration. In this calibration process, the image forming apparatus forms a toner pattern on the surface of the conveying belt and detects the density of the pattern using a sensor disposed in confrontation with the surface of the conveying belt. The image forming apparatus also has a cleaning unit disposed near the sensor and confronting the surface of the conveying belt for removing the toner pattern after calibration. The cleaning unit includes an electrostatic brush disposed in confrontation with the surface of the conveying belt and capable of applying a predetermined bias voltage, a secondary roller using electrostatic attraction to remove toner deposited on the electrostatic brush, and a waste toner box encompassing the electrostatic brush and secondary roller for collecting waste toner.